Biological information monitoring system

ABSTRACT

There is provided a biological information monitoring system for monitoring a biological information on a subject on a bed. The system includes a plurality of load detectors which are to be placed in the bed or under legs of the bed, and which are configured to detect a load of the subject; a load separation unit configured to separate a load component which oscillates according to a heartbeat of the subject, from the load of the subject; and a center of gravity position calculation unit configured to obtain a position of a center of gravity of the subject based on the load component which oscillates according to the heartbeat of the subject.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of InternationalApplication No. PCT/JP2017/018543 claiming the conventional priority ofJapanese patent Application No. 2016-101355 filed on May 20, 2016, andtitled “BIOLOGICAL INFORMATION MONITORING SYSTEM”. The disclosures ofJapanese patent Application No. 2016-101355, and InternationalApplication No. PCT/JP2017/018543 are incorporated herein by referencein their entirety.

BACKGROUND

The present disclosure relates to a biological information monitoringsystem for monitoring biological information of a subject (a humansubject).

Biological information of a subject is one of the important pieces ofinformation for knowing the physical condition (body condition) of apatient or a care receiver in the sites of the medical treatment and thecare. For example, the respiratory condition (respiratory state) of thesubject is grasped and can be utilized to grasp the symptoms of, forexample, the sleep apnea syndrome (SAS) and the snore; and to improve(alleviate) the symptoms.

It has been suggested that load sensors are arranged under legs of a bedto measure the respiratory condition of a subject on the basis ofmeasured values of the load sensors (Japanese Patent No. 4883380).Further, it has been also suggested that load detectors are arrangedunder legs of a bed to acquire (obtain) the movement of the center ofgravity of a subject living body on the bed so that the respiratorymovement (breathing movement) and the heartbeat movement of the subjectliving body are acquired on the basis of the movement of the center ofgravity (Japanese Publication of Examined Patent Application No.61-24010).

CITATION LIST SUMMARY

In the sites of the medical treatment, it is desired to accurately graspthe center of gravity position of a subject on a bed; however, theinventions described in Japanese Patent No. 4883380 and JapanesePublication of Examined Patent Application No. 61-24010 fail to meetsuch on-site demands.

An object of the present disclosure is to provide a biologicalinformation monitoring system which enables to grasp a center of gravityposition of a subject on a bed accurately.

According to a first aspect of the present disclosure, there is provideda biological information monitoring system for monitoring a biologicalinformation on a subject on a bed, the system including: a plurality ofload detectors which are to be placed in the bed or under legs of thebed, and which are configured to detect a load of the subject; a loadseparation unit configured to separate a load component which oscillatesaccording to a heartbeat of the subject, from the load of the subject;and a center of gravity position calculation unit configured to obtain aposition of a center of gravity of the subject based on the loadcomponent which oscillates according to the heartbeat of the subject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting a configuration of a biologicalinformation monitoring system according to an embodiment of the presentdisclosure.

FIG. 2 is an illustrative view depicting an arrangement of loaddetectors with respect to a bed.

FIG. 3 is a flow chart depicting a center of gravity locus (trajectorypath) calculation method according to the embodiment of the presentdisclosure.

FIG. 4 is an illustrative view depicting an arrangement of four loaddetection areas defined on the upper surface of the bed.

FIG. 5 depicts exemplary load signals fed from the load detectors.

FIG. 6 depicts exemplary locus of the center of gravity of a subject.

FIG. 7 is a flow chart depicting a method for calculating the center ofgravity position of a subject on the basis of the respiration componentor the heartbeat component which has been separated from each loadsignal.

FIG. 8 is a block diagram depicting an entire configuration of a bedsystem according to a modified embodiment.

EMBODIMENTS First Embodiment

A first embodiment of the present disclosure will be explained withreference to FIGS. 1 to 7.

As depicted in FIG. 1, a biological information monitoring system(respiratory waveform drawing system, respiratory information acquiringsystem) 100 of this embodiment is provided to perform the observationand the measurement in order to grasp the biological state or conditionof a subject (a human subject, that is, a person being monitored) on abed. The biological information monitoring system 100 principallyincludes a load detecting unit 1, a control unit (a controller) 3, astorage unit (a storage) 4, and a display unit (a display) 5. The loaddetecting unit 1 and the control unit 3 are connected via an A/Dconverting unit 2. A notification unit 6 and an input unit 7 are furtherconnected to the control unit 3.

The load detecting unit 1 is provided with four load detectors 11, 12,13, 14. Each of the load detectors 11, 12, 13, 14 is a load detectorwhich detects the load by using, for example, a beam-type load cell.Such a load detector is described, for example, in Japanese Patent No.4829020 and Japanese Patent No. 4002905. Each of the load detectors 11,12, 13, 14 is connected to the A/D converting unit 2 by means of wiring.

The four load detectors 11, 12, 13, 14 of the load detecting unit 1 arearranged under the legs of a bed to be used by the subject.Specifically, as depicted in FIG. 2, the load detectors 11, 12, 13, 14are arranged respectively on the undersides of casters C₁, C₂, C₃, C₄attached to lower end portions of the legs disposed at the four cornersof the bed BD.

The A/D converting unit 2 is provided with an A/D converter whichconverts the analog signal fed from the load detecting unit 1 into thedigital signal. The A/D converting unit 2 is connected to each of theload detecting unit 1 and the control unit 3 by means of wiring.

The control unit 3 is an exclusive or general-purpose computer. Afrequency analysis unit (a frequency analyzer) 31, a signal separationunit (a signal separator) (a load separation unit, or a load separator)32, a center of gravity position calculation unit (a center of gravityposition calculator) 33, and a biological information analysis unit (abiological information analyzer) (presence-on-bed determination unit) 34are constructed therein.

The storage unit 4 is a storage device which stores the data used forthe biological information monitoring system 100. For example, it ispossible to use a hard disk (magnetic disk) therefore. The display unit5 is a monitor, such as a liquid crystal monitor, for displaying theinformation outputted from the control unit 3 for a user of thebiological information monitoring system 100.

The notification unit 6 is provided with a device for visually orauditorily performing predetermined notification on the basis of theinformation fed from the control unit 3, for example, a speaker. Theinput unit 7 is an interface for performing predetermined input for thecontrol unit 3, and may be a keyboard and a mouse.

It is possible to detect and monitor various biological information,such as the respiratory condition of the subject on the bed, by usingthe biological information monitoring system 100 described above. Theacquisition and the monitoring of various biological information areperformed on the basis of the variation of the center of gravityposition of the subject on the bed.

An explanation will be given about the operation for calculating thecenter of gravity position of the subject on the bed, by using thebiological information monitoring system 100. As depicted in FIG. 3, thecalculation of the center of gravity position of the subject, which isbased on the use of the biological information monitoring system 100,includes a load detecting step (S01) of detecting the load of thesubject and a center of gravity locus calculating step (S02) ofcalculating the temporal variation of the position of the center ofgravity of the subject (center of gravity locus) on the basis of thedetected load.

In the load detecting step S01, the load of the subject S on the bed BDis detected, by using the load detectors 11, 12, 13, 14. As the loaddetectors 11, 12, 13, 14 are arranged respectively on the undersides ofthe casters C₁, C₂, C₃, C₄ as described above, the load, which isapplied to the upper surface of the bed BD, is detected in a dispersedmanner by the four load detectors 11, 12, 13, 14. Specifically, asdepicted in FIG. 4, the rectangular upper surface of the bed BD islongitudinally divided into two and laterally divided into two, and thusthe upper surface is equally divided into four rectangular areas I toIV.

Accordingly, the load, which is applied to the area I positioned withthe left lower half of the body of the subject S lying on his/her back(face up) at the central portion of the bed BD, is principally detectedby the load detector 11, and the load, which is applied to the area IIpositioned with the right lower half of the body of the subject S in thesame state, is principally detected by the load detector 12. Similarly,the load, which is applied to the area III positioned with the rightupper half of the body of the subject S lying on his/her back at thecentral portion of the bed BD, is principally detected by the loaddetector 13, and the load, which is applied to the area IV positionedwith the left upper half of the body of the subject S in the same state,is principally detected by the load detector 14. Note that when thesubject S does not exist on the bed BD, the total of the outputs fromthe load detectors 11, 12, 13, 14 represents the weight of the beditself. When the subject S exists on the bed BD, the total of theoutputs from the load detectors 11, 12, 13, 14 represents the weight ofthe bed and the body weight of the subject S. Therefore, it is possibleto measure the body weight of the subject S when the subject S exists onthe bed, by previously storing the weight of the bed itself in thestorage unit 4. Note that when the weight of the bed is not uniformamong the four areas, the difference therebetween is stored beforehandas the bed weight corresponding to each of the load detectors. Further,it is desirable that the situation in which any weight other than thatof the subject S is brought about during the actual measurement, forexample, the placement of any bedding, any baggage or the like isreflected to the weight of the bed.

Each of the load detectors 11, 12, 13, 14 detects the load (loadchange), and the load (load change) is outputted as the analog signal tothe A/D converting unit 2. The A/D converting unit 2 converts the analogsignal into the digital signal (hereinafter referred to as “loadsignal”) while using the sampling period of, for example, 5milliseconds, and the load signal is outputted to the center of gravityposition calculation unit 33 not through the frequency analysis unit 31and the signal separation unit 32.

Exemplary load signals are depicted in FIG. 5. FIG. 5 depicts the loadsignals s₁ (solid line), s₂ (broken line), s₃ (alternate long and shortdash line), and s₄ (alternate long and two short dashes line) fed fromthe load detectors 11, 12, 13, 14 as outputted during the period rangingfrom the time t₁₀ to the time t₁₄. The following fact has been observed.That is, the subject S lay on his/her back at the central portion of thebed BD as depicted in FIG. 4 during the period ranging from the time t₁₀to the time t₁₁ (period F₁₁). The subject S moved to the side of theareas I, IV of the bed BD during the period ranging from the time t₁₁ tothe time t₁₂ (period P₁₂). The subject S moved to some extent to thecentral side of the bed BD during the period ranging from the time t₁₂to the time t₁₃ (period P₁₃) as compared with the period P₁₂. Thesubject S lay on his/her back at the central portion of the bed BDduring the period ranging from the time t₁₃ to the time t₁₄ (periodP₁₄).

During the period P₁₁, the subject S lay on his/her back at the centralportion of the bed BD as depicted in FIG. 4. Therefore, during theperiod P₁₁, the signals s₃, s₄, which are fed from the load detectors13, 14 arranged on the head side of the subject S, are approximatelyequal to one another, and the signals s₁, s₂, which are fed from theload detectors 11, 12 arranged on the foot side of the subject S, areapproximately equal to one another.

During the period P₁₂, the subject S moved to the side of the areas I,IV of the bed BD. Therefore, during the period P₁₂, the signals s₁, s₄,which are fed from the load detectors 11, 14 arranged in the areas I,IV, exhibit the large load values as compared with the period P₁₁, andthe signals s₂, s₃, which are fed from the load detectors 12, 13arranged in the areas II, III, exhibit the small load values as comparedwith the period P₁₁.

During the period P₁₃, the subject S moved to some extent to the centralside of the bed BD as compared with the period P₁₂. Therefore, duringthe period P₁₃, the signals s₁, s₄, which are fed from the loaddetectors 11, 14 arranged in the areas I, IV, exhibit the small loadvalues as compared with the period P₁₂, and the signals s₂, s₃, whichare fed from the load detectors 12, 13 arranged in the areas II, III,exhibit the large load values as compared with the period P₁₂.

During the period P₁₄, the subject S lay on his/her back at the centralportion of the bed BD in the same manner as the period P₁₁. Therefore,during the period P₁₄, the signals s₁ to s₄, which are provided duringthe period P₁₄, are the same as the signals s₁ to s₄ provided during theperiod P₁₁.

In the center of gravity locus calculating step S02, the center ofgravity position calculation unit 33 calculates the position G (X, Y) ofthe center of gravity G of the subject S on the bed BD at apredetermined period T (for example, a period equal to the samplingperiod of 5 milliseconds described above) on the basis of the loadsignals s₁ to s₄ fed from the load detectors 11 to 14 to acquire(obtain) the temporal variation of the position of the center of gravityG of the subject S (center of gravity locus GT). In this case, (X, Y)indicates the coordinates on the XY coordinate plane in which X extendsin the longitudinal direction of the bed BD and Y extends in the lateraldirection of the bed BD while the central portion of the bed BD is theorigin (FIG. 6).

The calculation of the position G (X, Y) of the center of gravity G bythe center of gravity position calculation unit 33 is performed inaccordance with the following operation. That is, G (X, Y) is calculatedin accordance with the following expressions assuming that thecoordinates of the load detectors 11, 12, 13, 14 are (X₁₁, Y₁₁), (X₁₂,Y₁₂), (X₁₃, Y₁₃), and (X₁₄, Y₁₄) respectively, and the detection valuesof the load detectors 11, 12, 13, 14 are W₁₁, W₁₂, W₁₃, and W₁₄respectively.

$\begin{matrix}{X = \frac{{X_{11} \times W_{11}} + {X_{12} \times W_{12}} + {X_{13} \times W_{13}} + {X_{14} \times W_{14}}}{W_{11} + W_{12} + W_{13} + W_{14}}} & ( {{Numerical}\mspace{14mu} {expression}\mspace{14mu} 1} ) \\{Y = \frac{{Y_{11} \times W_{11}} + {Y_{12} \times W_{12}} + {Y_{13} \times W_{13}} + {Y_{14} \times W_{14}}}{W_{11} + W_{12} + W_{13} + W_{14}}} & ( {{Numerical}\mspace{14mu} {expression}\mspace{14mu} 2} )\end{matrix}$

The center of gravity position calculation unit 33 acquires the temporalvariation of the position G (X, Y) of the center of gravity G, i.e., thecenter of gravity locus GT while calculating the position G (X, Y) ofthe center of gravity G at the predetermined sampling period T on thebasis of the numerical expressions (1) and (2) described above. Theacquired center of gravity locus GT is stored, for example, in thestorage unit 4.

An example of the center of gravity locus GT calculated by the center ofgravity position calculation unit 33 is depicted in FIG. 6. FIG. 6depicts the positions G (X_(P11), Y_(P1)), G (X_(P12), Y_(P12)), G(X_(P13), Y_(P13)) of the center of gravity G of the subject S on thebed BD at the time t₁₁₀, t₁₂₀, t₁₃₀ included in the periods P₁₁, P₁₂,P₁₃ depicted in FIG. 5 respectively. An arrow of alternate long andshort dash line to connect these positions indicates the center ofgravity locus GT of the center of gravity G of the subject S moving fromthe position G (X_(P11), Y_(P11)) to G (X_(P13), Y_(P13)).

In this embodiment, the biological information analysis unit 34 analyzesthe presence or absence of a body motion of the subject S and the mannerof a body motion of the subject S on the basis of the center of gravitylocus GT of the subject S calculated as above by the center of gravityposition calculation unit 33. Specifically, for example, the biologicalinformation analysis unit 34 calculates the movement speed (movementamount per unit time) of the center of gravity G on the basis of thechanges in the position of the center of gravity G of the subject S atthe respective points in time, stored in the storage unit 4, and whenthe calculated speed exceeds a predetermined threshold, the biologicalinformation analysis unit 34 determines that the subject S has performeda body motion. Note that a body motion of the subject S includes a bodymotion caused by a relatively large movement of the body involving themovement of the body portion (body trunk) of the subject S (large bodymotion), such as turning over, and a body motion caused by a relativelysmall movement of the body not involving the movement of the bodyportion of the subject S (small body motion), such as movement of hands,feet, and/or face. A large body motion is, specifically, turning over,sitting up or the like. When a large body motion occurs to the subject,the direction of the body axis of the subject (the direction in whichthe backbone of the subject extends) changes in general. A small bodymotion is, specifically, for example, the movement only of hands, feet,and/or head.

When the large body motion is defined in view of the manner of thetemporal variation of the position of the center of gravity, the largebody motion can be defined in general to be the movement of the centerof gravity for a relatively long distance exceeding a predetermineddistance, which occurs within a predetermined time period.Alternatively, it is also possible to define, on the basis of thedifference from the temporal variation of the position of the center ofgravity caused by the small body motion, for example, that the largebody motion is the body motion in which the center of gravity is moved,within a predetermined time period, at least nearly predetermined timesas greatly as the movement distance of the center of gravity by thesmall body motion. Further, it is also allowable to define, by comparingwith the amplitude of the respiratory oscillation as described later on.

When the small body motion is defined in view of the manner of thetemporal variation of the position of the center of gravity, the smallbody motion can be defined in general to be the movement of the centerof gravity for a relatively short distance within a predetermined timeperiod. Further, it is also allowable to define, by comparing with theamplitude of the respiratory oscillation as described later on. Further,it is also allowable to define that the small body motion is the bodymotion to cause the movement of the center of gravity for a relativelyshort distance within a predetermined time period, the movement of thecenter of gravity not being an oscillation in a constant direction.According to this definition, when an attention is paid to the movementof the center of gravity, it is possible to further clearly distinguishthe small body motion from the respiration.

Here, in the center of gravity locus calculating step S02, as depictedin the numerical expressions (1) and (2) described above, the center ofgravity position G (X, Y) is calculated on the basis of the entire loadsW₁₁, W₁₂, W₁₃, and W₁₄ detected by the load detectors 11, 12, 13, 14respectively. Accordingly, for example, when any object is placed in aposition away from the subject S on the bed, the center of gravityposition G (X, Y) calculated by the numerical expressions (1) and (2)described above may be displaced (deviated) from the actual center ofgravity position of the subject 5, by the influence of the load of theobject which has been placed on the bed. For this reason, in thisembodiment, the components included in a specified frequency range(band) are separated from each of the load signals s₁ to s₄ outputtedfrom the load detectors 11 to 14 to also calculate the center of gravityposition of the subject S on the basis of the separated components.

In the following, with reference to the flow chart in FIG. 7, anexplanation will be given about the process of separating the componentsincluded in the frequency range of respiration (about 0.2 Hz to about0.33 Hz) from each of the load signals s₁ to s₄, and calculating thecenter of gravity position of the subject S on the basis of theseparated components.

In a frequency analyzing step S10, the frequency analysis unit 31acquires a frequency spectrum by performing the Fourier transformationof each or at least one of the load signals s₁ to s₄ outputted from theload detectors 11 to 14.

In a signal separating step S20, the signal separation unit 32 specifiesa peak frequency included in the frequency range of respiration (i.e.,frequency of the respiration of the subject S) based on the frequencyspectrum acquired in the frequency analyzing step S10. Then, the signalseparation unit 32 separates components s_(b1) to s_(b4) (hereinafterreferred to as “respiration components”), corresponding to the specifiedpeak frequency, from the load signals s₁ to s₄ respectively.

In a center of gravity position calculating step S30, the center ofgravity position calculation unit 33 calculates the center of gravityposition G_(b) (X, Y) of the subject S on the bed in accordance with thenumerical expressions (1) and (2) described above, on the basis of therespiration components s_(b1) to s_(b4) separated in the signalseparating step 20.

In a biological information analyzing step S40, the biologicalinformation analysis unit 34 may adopt either of the center of gravityposition G (X, Y) calculated on the basis of the entire loads and thecenter of gravity position G_(b) (X, Y) (respiratory center of gravity,center of gravity of respiration) calculated on the basis of therespiration components s_(b1) to s_(b4). For example, after comparisonof the center of gravity position G (X, Y) calculated on the basis ofthe entire loads with the center of gravity position G_(b) (X, Y)calculated on the basis of the respiration components s_(b1) to s_(b4),the biological information analysis unit 34 may determine which to adoptas the center of gravity position of the subject S. Alternatively, thedistance between the center of gravity position G (X, Y) based on theentire loads and the center of gravity position G_(b) (X, Y) based onthe respiration components is calculated, and when the calculateddistance exceeds a predetermined range, the biological informationanalysis unit 34 may adopt the center of gravity position G_(b) (X, Y)based on the respiration components as the center of gravity position ofthe subject S. In this case, the predetermined range may beappropriately set in consideration of, for example, the dimension(s) ofthe bed, the body height and weight of the subject S, and the like.

The biological information analysis unit 34 analyzes various biologicalinformation of the subject S by using the adopted center of gravityposition.

By the way, the respiration of human is performed by moving the chestand the diaphragm to expand and shrink the lungs. In this context, whenthe air is inhaled, i.e., when the lungs are expanded, the diaphragm islowered downwardly, and the internal organs are also moved downwardly.On the other hand, when the air is expired, i.e., when the lungs areshrunk, the diaphragm is raised upwardly, and the internal organs arealso moved upwardly. As a result of the research performed by theinventors of the present disclosure, it has been found out that inaccordance with the movement of the internal organs, the center ofgravity G oscillates approximately along the extending direction of thebackbone (body axis direction) (hereinafter referred to as “respiratoryoscillation”).

Therefore, when the center of gravity position is subject to therespiratory oscillation in a specified direction, the biologicalinformation analysis unit 34 regards the specified direction as thedirection of the body axis of the subject S, and determines the postureof the subject S on the bed (whether the body axis is parallel to thelongitudinal direction of the bed or inclined with respect to thelongitudinal direction of the bed). The direction of the respiratoryoscillation can be specified, for example, by specifying a certainextreme point (extreme value point) and an extreme point appearingimmediately before or immediately after the certain extreme point fromthe locus of the respiration oscillation, and acquiring the axisconnecting both of the extreme points.

Further, the biological information analysis unit 34 draws a respiratorywaveform of the subject S with a longitudinal axis as a direction of thebody axis and a lateral axis as a time axis, by plotting distances, eachbetween the center of oscillation of the respiratory oscillation and theposition obtained by projecting the center of gravity position at eachpoint in time to the body axis. Then, the biological informationanalysis unit 34 counts the number of maximum values or minimum valuesappearing on the respiratory waveform to thereby determine therespiration rate of the subject S. Furthermore, based on the amplitudeof the center of gravity position (i.e., amplitude of the respiratoryoscillation, or amplitude of the respiratory waveform), the biologicalinformation analysis unit 34 calculates a respiratory ventilation volume(tidal volume) per one respiration of the subject S (depth of therespiration).

Next, with reference to the flow chart in FIG. 7, an explanation will begiven about the process of separating the components included in thefrequency range of heartbeat (about 0.5 Hz to about 3.3 Hz; hereinafterreferred to as “heartbeat range”) from each of the load signals s₁ tos₄, and calculating the center of gravity position of the subject S onthe basis of the separated components. Note that this process may becarried out in parallel to the calculation of the center of gravityposition G_(b) (X, Y) based on the respiration components describedabove, or may be solely carried out.

In the frequency analyzing step S10, the frequency analysis unit 31acquires a frequency spectrum in the heartbeat range, by performing theFourier transformation of each or at least one of the load signals s₁ tos₄ outputted from the load detectors 11 to 14.

In the signal separating step S20, the signal separation unit 32specifies a peak frequency included in the heartbeat range (i.e.,frequency of the heartbeat of the subject S) based on the frequencyspectrum acquired in the frequency analyzing step S10. Then, the signalseparation unit 32 separates the components s_(h1) to s_(h4)(hereinafter referred to as “heartbeat components”), corresponding tothe specified peak frequency, from each of the load signals s₁ to s₄.

In the center of gravity position calculating step S30, the center ofgravity position calculation unit 33 calculates the center of gravity Gof the subject S on the bed in accordance with the numerical expressions(1) and (2) described above, on the basis of the heartbeat componentss_(h1) to s_(h4) separated in the signal separating step 20 (hereinaftersuch center of gravity G referred to as “center of gravity G_(h) basedon the heartbeat components (heartbeat center of gravity, center ofgravity of heartbeat)”).

The center of gravity G_(h) based on the heartbeat components of thesubject S on the bed as calculated by using the heartbeat componentss_(h1) to s_(h4) separated from the load signals s₁ to s₄ have thefollowing characteristics.

(1) The center of gravity G_(h) based on the heartbeat components iscalculated by using only the heartbeat components s_(h1) to s_(h4),among the load signals s₁ to s₄, which oscillate corresponding to theheartbeat of the subject S. Consequently, for example, in the case thata load by a third party (such as a visitor) whose heartbeat has afrequency different from that of the heartbeat of the subject S, or aload by an inanimate object (such as a bag) having no heartbeat is addedon the bed BD, the center of gravity G_(h) based on the heartbeatcomponents remains unmoved, and the center of gravity G_(h) based on theheartbeat components moves only in the case that the subject S hasmoved.

(2) As a result of the observation, by the inventors of the presentdisclosure, of the locus of movement of the center of gravity G_(h)based on the heartbeat components, it has been found out that the centerof gravity G_(h) based on the heartbeat components slightly oscillatesalong the direction obtained by rotating the body axis of the subject Scounterclockwise to some degree. This oscillation (hereinafter referredto as “heartbeat oscillation”) is considered to be caused by the beatingof the heart.

In the biological information analyzing step S40, the biologicalinformation analysis unit 34 may compare the center of gravity positionG (X, Y) calculated on the basis of the entire loads with the positionof the center of gravity G_(h) based on the heartbeat components, anddetermine which to adopt as the center of gravity position of thesubject S. This determination can be made in accordance with the methodsame as or equivalent to the method explained above concerning thecenter of gravity position G_(b) (X, Y) based on the respirationcomponents.

Further, the biological information analysis unit 34 can also determinewhether or not the subject S exists on the bed BD, namely, make apresence-on-bed determination, on the basis of whether or not it ispossible to acquire the center of gravity G_(h) based on the heartbeatcomponents. When the subject S does not exist on the bed BD, thecomponents, which vary according to the heartbeat of the subject S, donot exist in each of the load signals s₁ to s₄ of the load detectors 11to 14. Consequently, it is not possible to separate such components, andit is not possible to calculate the center of gravity G_(h) based on theheartbeat components. For this reason, the presence-on-bed determinationcan be made on the basis of the presence or absence of the heartbeatcomponents or whether or not it is possible to calculate the center ofgravity G_(h) based on the heartbeat components. The biologicalinformation analysis unit 34 may determine that the subject S exists onthe bed, for example, when it is confirmed that the calculated center ofgravity G_(h) based on the heartbeat components exists on the bed BD.More precisely, when it is confirmed that the center of gravity G_(h)based on the heartbeat components is oscillating in a predetermineddirection which is inclined with respect to the body axis of the subjectS, the biological information analysis unit 34 may determine that thesubject S exists on the bed.

Furthermore, the biological information analysis unit 34 can acquire thedirection of the body axis of the subject S, on the basis of thedirection of oscillation of the center of gravity G_(h) based on theheartbeat components, and can also acquire a heart rate, on the basis ofthe oscillation rate per one minute of the center of gravity G_(h) basedon the heartbeat components.

The effects of the biological information monitoring system 100 of thisembodiment are summarized as follows.

The signal separation unit 32 of this embodiment separates, for example,the respiration components included in the frequency range ofrespiration and the heartbeat components included in the frequency rangeof heartbeat, from each of the load signals s₁ to s₄ outputted from theload detectors 11 to 14. Then, the center of gravity positioncalculation unit 33 of this embodiment calculates not only the center ofgravity position G (X, Y) calculated on the basis of the entire loads,but also the center of gravity position G_(b) (X, Y) based on therespiration components and the center of gravity position G_(h) (X, Y)based on the heartbeat components. Consequently, the biologicalinformation analysis unit 34 can utilize the center of gravity positionG_(b) (X, Y) based on the respiration components and the center ofgravity position G_(h) (X, Y) based on the heartbeat components foranalyzing various biological information of the subject S. The center ofgravity position G_(b) (X, Y) based on the respiration components andthe center of gravity position G_(h) (X, Y) based on the heartbeatcomponents remain unchanged when a load not deriving from the subject S,such as a load of baggage or a visitor, is added on the bed BD, so thatusing these center of gravity positions makes it possible to furtheraccurately analyze biological information of the subject S.

For example, by using the center of gravity position G_(b) (X, Y) basedon the respiration components, the biological information analysis unit34 can analyze the posture (body axis direction) of the subject S on thebed and the respiratory condition such as respiratory waveform(respiration waveform), respiratory rate (respiration rate), andrespiratory ventilation volume.

Further, based on the presence or absence of the heartbeat components orthe center of gravity G_(h) based on the heartbeat components, thebiological information analysis unit 34 can make a presence-on-beddetermination with respect to the subject S. Unlike the respiration, theheartbeat cannot be stopped consciously (deliberately, intentionally),and thus, present (exist, settling) on/leaving (absent) from the bed ofthe subject S can be further reliably determined, by making apresence-on-bed determination on the basis of the presence or absence ofthe heartbeat components or the center of gravity G_(h) based on theheartbeat components.

The biological information monitoring system 100 of this embodimentacquires biological information of the subject S by using the loaddetectors 11 to 14 arranged under the legs of the bed BD. Therefore, itis unnecessary to attach any measuring device to the body of the subjectS. Neither discomfort nor sense of incongruity is given to the subjectS.

Modified Embodiment

In the biological information monitoring system 100 of the embodimentdescribed above, the following modified embodiment may be adopted.

For example, the respiratory cycle (cycle of the respiration) differsdepending on the sex (gender), physique (physical constitution), lungcapacity and the like of a subject S, and the heartbeat cycle (cycle ofthe heartbeat) also differs from person to person. Consequently, when aplurality of subjects S exist on the bed BD, different peak frequenciesas many as the number of the subjects S appear in the frequency range ofrespiration and/or the frequency range of heartbeat in the frequencyspectrum acquired in the frequency analyzing step S10.

In view of the above, when a plurality of peak frequencies appear in thefrequency range of respiration and/or the frequency range of heartbeat,the signal separation unit 32 may determine that a plurality number ofsubjects S are on the bed, and separate the respiration componentsand/or the heartbeat components corresponding to each of the subjects S,from each of the load signals s₁ to s₄. Then, the center of gravityposition calculation unit 33 may calculate the center of gravityposition of each of the subjects S on the basis of the respirationcomponents and/or the heartbeat components corresponding to each of thesubjects S. For example, when a peak appears in each of a frequency v₁and a frequency v₂ in the frequency range of respiration, the signalseparation unit 32 determines that two subjects S are on the bed. In thesignal separating step S20, the signal separation unit 32 separates therespiration components corresponding to the frequency v₁ and therespiration components corresponding to the frequency v₂, from each ofthe load signals s₁ to s₄. Then, in the center of gravity positioncalculating step S30, the center of gravity position calculation unit 33calculates the center of gravity position G_(b1) (X, Y) based on therespiration components corresponding to the peak frequency v₁ and thecenter of gravity position G_(b2) (X, Y) based on the respirationcomponents corresponding to the peak frequency v₂.

According to the modified embodiment described above, even when aplurality number of subjects S are on the bed, it is possible toseparately acquire the center of gravity G_(b) based on the respirationof each of the subjects S and the center of gravity G_(h) based on theheartbeat of each of the subjects S, and the center of gravity positionof each of the subjects S can be accurately grasped.

In the biological information monitoring system 100 of the embodimentdescribed above, the biological information analysis unit 34 maydetermine that the subject S has settled on the bed, when the load addedto the bed BD increases by at least a predetermined value (for example,about 40 kg) and the heat beat components or the center of gravity G_(h)based on the heartbeat have/has been acquired. The biologicalinformation analysis unit 34 may determine that the subject S has leftthe bed, when the load added to the bed BD decreases by at least apredetermined value and the heat beat components or the center ofgravity G_(h) based on the heartbeat are/is unable to be acquired.

Note that when there exists on the bed BD an element striking the bed BDwith a predetermined period or cycle (impact element), waveform havingsuch predetermined period or cycle appears in each of the load signalss₁ to s₄ fed from the load detectors 11 to 14, four waveforms in theload signals s₁ to s₄ having phases identical to each other. If a loadcomponent including such waveform is separated by using the frequencyanalysis unit 31 and the signal separation unit 32, and the separatedload component is used for the center of gravity position calculationunit 33 to calculate a center of gravity position, it is possible tocalculate the center of gravity position of the impact element.

In the embodiment described above, each of the load detectors 11, 12,13, 14 is not limited to the load sensor having the beam-type load cell.It is also possible to use, for example, a force sensor.

In the embodiment described above, the number of load detectors is notlimited to four. It is also allowable to use five or more load detectorsby providing an additional leg or additional legs for the bed BD.Alternatively, it is also allowable to arrange the load detectors foronly three of the legs of the bed BD. Even when the three load detectorsare used, it is possible to detect a position of the center of gravity Gof the subject S on the plane of the bed BD provided that the three loaddetectors are not arranged on a straight line.

In the embodiment described above, the load detectors 11, 12, 13, 14 arearranged respectively on the undersides of the casters C₁, C₂, C₃, C₄attached to the lower ends of the legs of the bed BD. However, there isno limitation thereto. Each of the load detectors 11, 12, 13, 14 may beprovided respectively between one of the four legs of the bed BD and theboard of the bed BD. Alternatively, if each of the four legs of the bedBD can be divided into upper and lower portions, each of the loaddetectors 11, 12, 13, 14 may be provided between upper leg and lowerleg. Further alternatively, the load detectors 11, 12, 13, 14 may beformed integrally with the bed BD to construct a bed system BDScomprising the bed BD and the biological information monitoring system100 of this embodiment (FIG. 8). Note that in this specification, the“load detectors placed in the bed” means the load detectors each ofwhich is provided between one of the four legs of the bed BD and theboard of the bed BD as described above and the load detectors each ofwhich is provided between the upper leg and the lower leg.

In the embodiment described above, it is also allowable to provide asignal amplifying unit for amplifying the load signal fed from the loaddetecting unit 1 and/or a filtering unit for removing the noise from theload signal, between the load detecting unit 1 and the A/D convertingunit 2.

In the biological information monitoring system 100 of the embodimentdescribed above, the display unit 5 is not limited to the unit whichdisplays the information on the monitor so that the user can make thevisual recognition. For example, the display unit 5 may be a printerwhich periodically prints and outputs the respiratory condition(respiratory rate, respiratory ventilation volume), the state of theheartbeat, and the physical condition of the subject S. Alternatively,the display unit 5 may be a unit which performs the display by using anysimple visual expression, for example, such that a blue lamp is turnedON in the case of the presence-on-bed state and/or a red lamp is turnedON in the case of the bed-leaving state. Further alternatively, thedisplay unit 5 may be a unit which reports the biological information ofthe subject S to the user by means of any sound or voice. Furtheralternatively, it is also allowable that the biological informationmonitoring system 100 does not have the display unit 5. The biologicalinformation monitoring system 100 may have only an output terminal foroutputting the information. A monitor (display device) or the like,which is provided to perform the display, will be connected to thebiological information monitoring system 100 by the aid of the outputterminal.

The notification unit 6 of the embodiment described above performs thenotification auditorily. However, the notification unit 6 may beconstructed to perform the notification visually by means of, forexample, the flashing or flickering of light. Alternatively, thenotification unit 6 may be constructed to perform the notification bymeans of the vibration. Further, it is also allowable that thebiological information monitoring system 100 of the embodiment describedabove does not have the notification unit 6.

The present invention is not limited to the embodiments described aboveprovided that the feature of the present invention is maintained. Otherembodiments, which are conceivable within the scope of the technicalconcept of the present invention, are also included in the scope of thepresent invention.

The biological information monitoring system according to the aboveembodiments may further include a presence-on-bed determination unitconfigured to determine that the subject exists on the bed, based on theload component which oscillates according to the heartbeat of thesubject.

In the biological information monitoring system according to the aboveembodiments, the presence-on-bed determination unit may be configured todetermine that the subject has settled on the bed, based on the loadcomponent which oscillates according to the heartbeat of the subject andan increase, beyond a predetermined value, of a load applied onto thebed.

In the biological information monitoring system according to the aboveembodiments, the load separation unit may be configured such that, in acase that the subject is a plurality of subjects on the bed, the loadseparation unit separates the load of the subject into a plurality ofloads each corresponding to each of the plurality of subjects based on afrequency spectrum of a temporal variation of the load of the subjectdetected by at least one of the plurality of load detectors, andseparates a load component which oscillates according to a heartbeat ofeach of the plurality of subjects from each of the plurality of loads ofthe plurality of subjects, and the center of gravity positioncalculation unit may be configured to obtain a position of a center ofgravity of each of the plurality of subjects based on the load componentwhich oscillates according to the heartbeat of each of the plurality ofsubjects.

In the biological information monitoring system according to the aboveembodiments, the load separation unit may be further configured toseparate a load component which oscillates according to a respiration ofthe subject, from the load by the subject, and the center of gravityposition calculation unit may be further configured to obtain a positionof a respiratory center of gravity of the subject based on the loadcomponent which oscillates according to the respiration of the subject.

In the biological information monitoring system according to the aboveembodiments, the load separation unit may be configured such that, in acase that the subject is a plurality of subjects on the bed, the loadseparation unit separates the load of the subject into a plurality ofloads each corresponding to each of the plurality of subjects based on afrequency spectrum of a temporal variation of the load of the subjectdetected by at least one of the plurality of load detectors, andseparates a load component which oscillates according to a heartbeat ofeach of the plurality of subjects and a load component which oscillatesaccording to a respiration of each of the plurality of subjects, fromeach of the plurality of loads of the plurality of subjects, and thecenter of gravity position calculation unit may be configured to obtaina position of a heartbeat center of gravity of each of the plurality ofsubjects based on the load component which oscillates according to theheartbeat of each of the plurality of subjects, and obtain a position ofa respiratory center of gravity of each of the plurality of subjectsbased on the load component which oscillates according to therespiration of each of the plurality of subjects.

According to the biological information monitoring system of an aspectof the present disclosure, it is possible to grasp a center of gravityposition of the subject on the bed accurately.

1. A biological information monitoring system for monitoring abiological information on a subject on a bed, the system comprising: aplurality of load detectors which are to be placed in the bed or underlegs of the bed, and which are configured to detect a load of thesubject; a load separation unit configured to separate a load componentwhich oscillates according to a heartbeat of the subject, from the loadof the subject; and a center of gravity position calculation unitconfigured to obtain a position of a center of gravity of the subjectbased on the load component which oscillates according to the heartbeatof the subject.
 2. The biological information monitoring systemaccording to claim 1, further comprising a presence-on-bed determinationunit configured to determine that the subject exists on the bed, basedon the load component which oscillates according to the heartbeat of thesubject.
 3. The biological information monitoring system according toclaim 2, wherein the presence-on-bed determination unit is configured todetermine that the subject has settled on the bed, based on the loadcomponent which oscillates according to the heartbeat of the subject andan increase, beyond a predetermined value, of a load applied onto thebed.
 4. The biological information monitoring system according to claim1, wherein the load separation unit is configured such that, in a casethat the subject is a plurality of subjects on the bed, the loadseparation unit separates the load of the subject into a plurality ofloads each corresponding to each of the plurality of subjects based on afrequency spectrum of a temporal variation of the load of the subjectdetected by at least one of the plurality of load detectors, andseparates a load component which oscillates according to a heartbeat ofeach of the plurality of subjects from each of the plurality of loads ofthe plurality of subjects, and the center of gravity positioncalculation unit is configured to obtain a position of a center ofgravity of each of the plurality of subjects based on the load componentwhich oscillates according to the heartbeat of each of the plurality ofsubjects.
 5. The biological information monitoring system according toclaim 1, wherein the load separation unit is further configured toseparate a load component which oscillates according to a respiration ofthe subject, from the load of the subject, and the center of gravityposition calculation unit is further configured to obtain a position ofa respiratory center of gravity of the subject based on the loadcomponent which oscillates according to the respiration of the subject.6. The biological information monitoring system according to claim 5,wherein the load separation unit is configured such that, in a case thatthe subject is a plurality of subjects on the bed, the load separationunit separates the load of the subject into a plurality of loads eachcorresponding to each of the plurality of subjects based on a frequencyspectrum of a temporal variation of the load of the subject detected byat least one of the plurality of load detectors, and separates a loadcomponent which oscillates according to a heartbeat of each of theplurality of subjects and a load component which oscillates according toa respiration of each of the plurality of subjects, from each of theplurality of loads of the plurality of subjects, and the center ofgravity position calculation unit is configured to obtain a position ofa heartbeat center of gravity of each of the plurality of subjects basedon the load component which oscillates according to the heartbeat ofeach of the plurality of subjects, and obtain a position of arespiratory center of gravity of each of the plurality of subjects basedon the load component which oscillates according to the respiration ofeach of the plurality of subjects.